1. Field of the Invention
The present invention relates to optical devices for varying the power of light propagating from a first optical path to a second optical path, and to movable reflectors used in such optical devices.
2. Related Background Art
Optical communications are often performed using optical devices, e.g., variable optical attenuators or optical switches, for adjusting the power of optical signals propagating in optical waveguides. An example of such optical devices is disclosed in C. Marxer et al., “Micro-Opto-Mechanical 2×2 Switch for Single Mode Fibers based on Plasma-Etched Silicon Mirror and Electrostatic Actuation” (preceding 11th IEEE Workshop on Micro-Electro-Mechanical System, 1998, pp 233–237). In this example, a mirror is placed in an optical path from a first optical waveguide to a second optical waveguide, and the mirror is moved to vary the quantity of light reflected by the mirror, thereby adjusting the power of the light fed from the first optical waveguide into the second optical waveguide.
FIG. 1 is a schematic plan view showing an example of a variable optical attenuator using a movable mirror. The variable optical attenuator 50 has a Planar Lightwave Circuit (PLC) 10, a movable mirror 20, and a mirror driver device 30. Optical waveguides 11 and 12 in PLC 10 have their respective ends arranged in mirror symmetry with respect to a reference plane 13. These ends have respective end faces 11a and 12a aligned on an identical plane. The movable mirror 20 has a reflecting surface 20a parallel to these end faces 11a and 12a. The mirror driver device 30 can move the movable mirror 20 along directions indicated by arrows 32 and 33. When light from the optical waveguide 11 is incident onto the reflecting surface 20a, it is reflected toward the optical waveguide 12. This causes the light to propagate from the optical waveguide 11 to the optical waveguide 12. On the other hand, when the light from the optical waveguide 11 is not incident onto the reflecting surface 20a, the light does not enter the optical waveguide 12.
As shown in FIG. 1, the movable mirror 20 has an edge 20b. At the edge 20b the incident light is scattered into various directions by virtue of diffraction. For this reason, part of the light from the optical waveguide 11 returns to the optical waveguide 11, and again propagates in the optical waveguide 11. This light is optical feedback to the optical waveguide 11. Likewise, light emerging from the optical waveguide 12 is also scattered by the edge 20b and part thereof returns to the optical waveguide 12. Such optical feedback deforms the waveform of the signal light propagating in the optical waveguides 11 and 12, so as to cause communication error in certain cases.